Direct-print light-developable emulsion containing silver halide grains sensitized on the surface with silver thiocyanate,iodide and gold compound

ABSTRACT

A PHOTOGRAPHIC EMULSION OF THE SILVER HALIDE DIRECTPRINT LIGHT-DEVELOPABLE TYPE CONTAINING SILVER THIOCYANATE, OPTIMUM RESULTS MAY BE OBTAINED BY ADDITION OF IODIDE AND GOLD SENSTITIZERS.

United States Patent 3,782,960 DIRECT-PRINT LIGHT-DEVELOPABLE EMULSION CONTAINING SILVER HALIDE GRAINS SENSI- TIZED ON THE SURFACE WITH SILVER THIO- CYANATE, IODIDE AND GOLD COMPOUND David W. Walters, Williamson, Robert E. Heeks, Penfield, and Donald P. Sullivan, Rochester, N.Y., assignors to Xerox Corporation, Stamford, Conn. No Drawing. Filed Mar. 18, 1971, Ser. No. 125,816 Int. Cl. G03c 1/28 US. Cl. 96-108 3 Claims ABSTRACT OF THE DISCLOSURE A photographic emulsion of the silver halide directprint light-developable type containing silver thiocyanate. Optimum results may be obtained by addition of iodide and gold sensitizers.

BACKGROUND OF THE INVENTION This invention relates in general to photographic emulsions. More specifically, the invention concerns photographic emulsions of the direct-print light-developable type.

The term direct-print light-developable refers to layers, generally deposited on a film or paper substrate, containing photosensitive materials upon which a visible image is obtained after an initial exposure to a pattern of high intensity light or other electromagnetic radiation has been utilized to form a latent image; the visible image being obtained by additional overall exposure to generally lower intensity radiation. This additional exposure is known as latentsiflcation. The entire sheet surface is exposed including exposure of the background area and re-exposure of the area upon which the initial image was formed. Direct-print light-developable materials are distinguished fiom developing-out emulsions in that they do not require a wet development treatment, such as a multistep chemical development after initial exposure to produce a visible image. While the direct-print light-develop able materials of this invention may be used for ordinary photographic purposes, they are particularly sensitive to a high intensity beam of light or other electromagnetic radiation and are, therefore, especially useful in high speed recording such as oscillographic recording and the like.

Direct-print light-developable type materials are today in general use for recording of oscillographic traces. However, the direct-print light-developable materials of the prior art are not entirely satisfactory for this recording purpose for a number of reasons. For example, it is generally true that the prior art materials which exhibit high sensitivity to an exposure of short duration to a high intensity beam tend to exhibit a correspondingly low degree of background stability. The latentsification procedure for these materials is highly critical and accordingly is exceedingly difiicult to carry out. The latent image may be entirely lost during the latentsification operation where the background darkens too rapidly. In other cases, a phenomenon known as reversal may occur, this being a darkening of the background which proceeds at a more rapid rate than darkening of the image trace. In these situations, the trace may be temporarily or permanently obscured. Conversely, materials which exhibit a high de- "gree of background stability tend to exhibit a correspondingly low degree of sensitivity to the recording beam and, thus, the minimum exposure time is far above that desired for use in modern recording instruments.

Sensitized direct-print light-developable materials have been described by Byrne in US. Pat. 3,123,474 which describes sensitizing a silver halide emulsion with a comice bination of a plumbous salt and a. thiourea, thiosemicarbazide or mercapto succinic acid. While this material shows increased sensitivity, it is not as stable when exposed for prolonged times to daylight or normal room lighting as would be desirable. Upon prolonged exposure to ordinary illumination, the background darkens and the image regresses depending upon the viewing conditions which reduces the ratio between background and image density.

On occasion it is desirable to make a truly permanent record of an oscillographic trace. In this circumstance, it is desirable to develop the usual direct-print light-developable emulsion either before or after latentsification by chemical developing-out techniques. Many conventional direct-print light-developable emulsions require special developing materials and procedures. Preferably, a direct-print light-developable emulsion used in an oscillographic recorder should be developable by the usual direct-print light-developable techniques or alternatively, by means of a chemical developing-out process.

Diflferent direct-print light-developable materials produce image traces and background areas of varying colors. Typically, the image trace may be developed as a brown or blue-grey line. The background areas which would preferably remain white often acquire a uniform color, typically, pink, brown or blue. Preferably, there should be good contrast between the trace and backgrounds both in density and in color to permit convenient and accurate examination and evaluation of the trace.

It is also desirable to have access to the information recorded on the material as rapidly as possible. The access time is the period of time which elapses between the imagewise exposure and the first appearance of the recorded information in response to latentsification.

Thus, there is a continuing need for improved directprint light-developable materials having improved sensitivity, stability and appearance characteristics.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a direct-print light-developable emulsion overcoming the above-noted disadvantages.

Another object of this invention is to provide a novel light sensitive composition.

Another object of this invention is to provde a more sensitive dry process for the reproduction of images.

Still another object of this invention is to provide a photosensitive emulsion which may be developed either by direct-print light-developable techniques or by chemical developing-out techniques.

Still another object of this invention is to provide an improved direct-print light-developable emulsion which possesses both a high degree of photosensitivity and a high degree of background stability under general latentsification.

Another object of this invention is to provide a photosensitive emulsion which provides relatively improved access time.

A still further object of this invention is to provide a direct-print light-developable emulsion resistant to light degradation after imaging.

A further object of this invention is to provide a directprint light-developable emulsion which is capable of producing images having improved contrast and color characteristics.

The above objects and others are accomplished in accordance with this invention by providing a photographic direct-print light-developable emulsion comprising a photosensitive silver halide and gelatin containing silver thiocyanate as a sensitizer. Preferably, the emulsions also contain iodide and gold.

Good results have been obtained using from about 0.1 to 25 mole percent silver thiocyanate based on the silver in the silver halide grains. A higher degree of sensitization occurs when from about 0.01 to 25 mole percent iodide is added to the emulsion. Additional benefits primarily in reduced access time results from the addition of from about 0.001 to about 1.0 mole percent gold.

For high contrast, high photosensitivity, short access time, low background density and good background color, the amounts of sensitizing agents in the direct-print lightdevelopable emulsion (in mole percent per mole of silver in the layer) are: about 0.5 to about 9.0 mole percent silver thiocyanate, about 0.4 to mole percent iodide, and about 0.01 to 0.1 mole percent gold. The sensitizers may be added in any suitable form. The silver thiocyanate is added in the form of a gel suspension. Typically, gold and iodide are added as water soluble complexes or salts in water. However, this is not necessary. For example, some ingredients may be added as solids or in other solvents such as acids, bases or water miscible organic solvents.

As is further pointed out in the examples below, if no silver thiocyanate is added essentially no image is obtained. When silver thiocyanate alone is added, images are obtained which, however, have relatively high background, low contrast and long access time. The use of iodide alone provides images having low contrast and low sensitivity. The addition of silver thiocyanate to the emulsion containing iodide improves contrast; that is, the difference in density between the image area Dmux. and the density of the background areas D is greater. The difference between D and D is known as A D. It also improves sensitivity which increases the speed at which images may be recorded. Further, the addition of gold to the emulsions containing silver thiocyanate and iodide improves the access time as shown in copending application entitled D/ 3459, Print-Out Emulsion by Robert E. Heeks and Donald P. Sullivan, which is Ser. No. 98,057, filed Dec. 14, 1970, now abandoned.

The emulsion layer may comprise any suitable conventional silver halide and binder. Best results have been obtained with silver chlorobromide emulsions these are, therefore preferred. These emulsions are made by first forming silver chloride and then converting the silver chloride into silver bromide by adding a soluble bromide salt to the emulsion. Gelatin is the conventional binder for photographic emulsions. However, any other suitable binder, such as polyvinylalcohol, may be used if desired. Ordinarily, this layer should be no greater than about 25 microns in thickness. For optimum results, the layers should contain about three grams of elemental silver per square meter of coated emulsion. The emulsion layer may contain additional ingredients to enhance, synergize or otherwise modify its characteristics, as desired. Typical silver bromide emulsions are described in Photographic Emulsions, E. 1. Wall, American Photographic Publishing Company, Boston (1929) and in US. Pat. 3,249,440.

Silver thiocyanate is added to the emulsion in the form of a suspension, preferably about 0.6 mole AgCNS per liter of a gelatin suspension. The suspension is formed by adding silver nitrate to potassium thiocyanate in water. The precipitate is dispersed in a gelatin binder. Since the silver thiocyanate formed is light sensitive, the precipitation and subsequent process steps should be carried out under safelight conditions. The silver thiocyanate is added after the silver halide grains have been formed.

The iodide may be added in the form of any compound which will furnish iodide ions to the suspension and may be water soluble or insoluble. Typical compounds include lead iodide, silver iodide, alkali metal iodides, ammonium iodide, calcium iodide and barium iodide.

The gold may be added in the form of water soluble compounds such as ammonium aurothiocyanate, potassium aurothiocyanate, sodium aurothiocyanate, aurous thiosulfates, alkali metal aurous sulfates, chloroauric acid and alkali metal halides complexed with auric trihalides.

The iodide and gold are also added after the silver halide grains are formed. It is believed therefore that the sensitizers are primarily present on the surface of the silver halide grains. It is also believed that Whether the gold is added to the emulsion in the auric or the aurous form that it is converted to or remains aurous because of the presence of thiocyanate. It is believed this is true because the emulsions do not exhibit the characteristic dark delay improvement described in application Ser. No. 782,789, filed Dec. 12, 1968, now US. Pat. 3,660,100, which is typical of auric containing emulsions.

DESCRIPTION OF PREFERRED EMBODIMENTS The following examples further specifically define the present invention with respect to particular sensitizers and the amounts thereof used in the direct-print light-developable emulsions of this invention. All percentages used are mole percent per mole of silver in the silver halide grains unless otherwise indicated. The examples below utilizing sensitizers within the ranges described above are intended to illustrate various preferred embodiments of the direct-print light-developable emulsion of the present invention.

A gelatino-silver halide emulsion for use in the following examples with different amounts of different sensitizers is prepared as follows: An aqueous solution of silver nitrate is added to an aqueous gelatin solution of potassium chloride in such a manner that there is about mole percent of chloride ion based on the silver nitrate. The resulting mixture is ripened for about thirty minutes at about 160 F. Potassium bromide in an amount sufficient to provide about mole percent based on silver is then added. Ripening is continued for an additional 10 minutes.

The emulsion is then chilled, set, shredded and Washed to remove excess salts. This material is then melted at about 100 F., the sensitizers to be tested are then added and the mixture is ripened further. Before coating, an addition of about 15 mole percent potassium bromide is added. The emulsion is then coated onto a substrate to obtain a layer having about three grams of elemental silver per square meter.

The direct-print light-developable emulsions thus pro duced in each example are tested by exposing in an Edgerton, Germeshausen and Grier Mark VH Sensitometer at 100 microseconds exposure time. The test strips are exposed through a V2 stepwedge. After exposure the test strips are latentsified for about 10 minutes under General Electric Cool White Fluorescent lamps at an illuminational level of about 50 foot candles.

EXAMPLE I A silver halide emulsion prepared as described above is a tested without the addition of any of the sensitizers of this invention. No images are obtained.

EXAMPLE II In this experiment varying amounts of silver thiocyanate from about 1.0 mole percent to about 20 mole percent silver thiocyanate is added to the silver halide emulsion. Samples having different amounts of silver thiocyanates are tested as described above and the results are tabulated in Table I. As can be seen from Table I, a print-out effect was produced with this emulsion with fair images resultmg.

EXAMPLE III An emulsion is prepared and tested as described above with the addition of from about 0.2 to about 10.0 mole percent potassium iodide as the only sensitizer. The solution of potassium iodide in water is added as described above. The resulting test strips are tested as described above and the results shown in Table 1. As can be seen from Table I, images are obtained. The best results are obtained at 0.4 to with 5.6 mole percent potassium iodide being the optimum.

EXAMPLE IV In this experiment test emulsions are prepared using the The above test results were obtained using relatively small samples of photographic emulsion. When scaled up to production size quantities, it has been found that the optimum concentration of silver thiocyanate is about onefourth that of the laboratory scale optimum. The increase Optimum amount of the iodide sfinsitiler mole P 5 in sensitization obtained with larger batches is believed cent potassium iodide) with varying amounts f s er to be caused by a number of variables which have not thiocyanate- The test Strips are P p and tested as been duplicated in laboratory scale apparatus. For examdescribed above. As can be seen from the tabulation in ple, the scale up probably changes the average particle Table I, the addition of the silver thiocyanate to the op- 10 size, particle size distribution and ripening conditions timized iodide salt shows a dramatic increase in sensitivity caused by difierences in agitation and in heating and and overall image quality. Best results are obtained with cooling cycles between large and small batches. Further, from about to about mole percent silver y it is believed that silver thiocyanate reacts with the surnate- P ftfslllts are Obtainfid with abQllt 5 t0 9 H1016 face of the silver halide particles. Accordingly, the surpercent silver thmcyanate- 15 face area available to the silver 'thiocyanate affects this EXAMPLE v reaction. Sensitization will depend, therefor, on gel concentration, temperatures and ripening conditions and also Addmonal test smps are.pr?pared and tested usmg the on the particle size of the silver halide when the silver optimum amounts of the 10d1de salt (5.6 mole percent thbc n t i dd d Th f d f potassium iodide) and silver thiocyanate (8.0 mole perya a e S a e e Pre f quan lty 0 s1 Vet cent) with varying amounts of aurous thiocyanate. The ocyanate for large $9316 15 about 2 P P gold is added as described above The strips are Prepared based on the moles of s1lver 1n the silver halide grains. and tested as described above. As can be seen from Table Althougl} p i components and Proportions e I, there is a decrease in access time with the addition of e descrlbed m the above examples. other i le mathe gold. It is preferred that from about 0.01 to about 0.1 terlals. as listed above. y be us d with similar results. mole percent gold can be used, Optimum results are 0b- In addition, other materials may be added t0 the emulsion, tained using about 0.03 mole percent gold. layer to synergize, enhance or otherwise modify its proper- TABLE I [Sensltlzer (mole percent per mole silver)] Access time Image Example AgCNS Iodide Gold (seconds) Dmnx, Dmln AD rating 0.2 10 0.59 0.54 0.15 a 1. 0 10 0. 72 0. 55 0.15 4 5. 0 15 0. 70 0. 5s 0. 1s 5 10. 0 15 0. 74 0. 59 0. 15 3 IV 0. 1 5. 0 14. 0. 75 0. 5s 0. 17 5 1.0 5.5 15 0.77 0.59 0.18 5 3.0 5.0 14. 0.79 0.58 0.21 5 5.5 5.0 15 0.80 0. 58 0.22 7 8.0 5.5 15 0. s3 0. 58 0.25 s 15.0 5.5 15 0.80 0. 00 0.20 0 25. 0 5. 5 14 0. 79 0. 0. 19 5 V 3:8 21% ii 82?? 8:22 813i 1% s. 0 5. 0 10 o. 75 0. 0. 21 10 8.0 5.5 9 0.61 0. 42 0.19 s

As indicated by the above table, outstanding results are ties. For example, sensitizing dyes, various finishing aids obtained with a direct-print light-developable emulsion such as formaldehyde, surfactants, surface active agents sensitized with the sensitizing agents of the present insuch as saponin, humectants such as glycerin, stabilizers 'vention. In the above table columns 1 through 4 indicate 55 such as 7-hydroxy-5-methyl-1,3,4-triazoindolizine, matting the mole percents of silver thiocyanate, iodide, and gold, agents, etc., may be used in the emulsion layer. respectively. The fourth column gives the access time Other modifications and ramifications of the present inwhich is the amount of time required to produce a visible vention will occur to those skilled in the art upon a readimage upon latentsification. The fifth and sixth columns ing of the present disclosure. These are intended to be give the maximum image density and background density. included within the scope of this invention. The seventh column gives the density dilference which What is claimed is: indicates contrast between the image and background. The 1. A photosensitive direct-print light-developable emuleighth column gives an arbitrary image quality rating. sion comprising silver halide grains, a binder and from This rating varies from 0 to 10 with 0 indicating no image about 0.01 to about 25 mole percent iodide and from and 10 indicating an image of highest quality. Desirable about 0.001 to about 1.0 mole percent gold, based on the characteristics which are considered in establishing a ratmoles of silver in the silver halide grains, an effective ing for a given image incluude rate of latentsification to a quantity of silver thiocyanate, said silver thiocyanate, high image density, low background density, image sharpiodide and gold sensitizers being present on the surface of ness, apparent contrasts between image and background said silver halide grains. and background color and uniformity. Access time is in- 2. A photosensitive direct-print light-developable emulcluded. As can be seen from the table, the combination of sion comprising silver halide grains, a binder, and from optimal amounts of silver thiocyanate and iodide salt gives about 0.5 to about 9.0 mole percent silver thiocyanate, high image density and excellent contrast between image about 0.4 to about 10 mole percent iodide and about 0.01 and background. The further addition of gold greatly to about 0.1 mole percent gold based on the moles of decerascs access time.

silver halide grains said iodide, gold and silver thiocyanate 7 8 sensitizers being present on the surface of said silver 3,384,490 5/ 1968 Rees 96--108 halide grains. 3,260,605 7/1966 Sutherns 96-108 3. A photosensitive direct-print light-developable emul- 3,594,172 7/ 1971 Sincius 96108 sion comprising silver halide grains, a binder and about 2 2,597,856 5/1952 Damschroder 96108 mole percent silver thiocyanate, about 0.4 to about 10 5 2,222,262 11/1940 Leerrnakers 96-108 mole percent iodide, and about 0.01 to about 0.1 mole per- 2,222,264 11/ 1940 Neitz et a1. 96108 ment gold based on the moles of silver in said silver halide grains, said iodide, gold and silver thiocyanate sensitizers NORMAN, TORCHIN, Y EXamlIleI and being present on the surface of said silver halide LOWE, JR Assistant Examiner grains. 10

References Cited U.S. Cl. X.R.

UNITED STATES PATENTS 96107 3,507,656 4/1970 Sincius 95 10 ..."0.77".., and insert UNITED STATES PATENT OFFICE 7 CERTIFICATE OF CORRECTION 3,782, 960 Dated January 1, 1974 Patent No.

Robert F. Heeks, Donald P. Sullivan Inventor(s) David W. Walters,

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"Access Time" delete .--30-; under Column 5, Table I,

. .0" and insert Claim 1,

emulsion-.

insert -to sensitize said Signed and sealed this 23rd day of July 197b (SEAL) Attest: MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents 

